1. Field of the Invention
The invention relates generally to shock absorbers of the type that may be inserted in a drill or tubing string for the purpose of isolating downhole explosive shock and, more particularly, but not by way of limitation, it relates to an improved type of shock absorber for isolating the jarring effect from perforator jets located either upward or downward thereby to protect the delicate instrumentation of the pressure recording gauges.
2. Description of the Prior Art
A number of shock absorber devices have been devised for isolating vibrations or explosive energy from more sensitive instruments down within an oil well borehole. U.S. Pats. No. 4,817,710 and No. 4,693,317, related applications, teach a borehole shock absorber that is used for guarding against both longitudinal and radial shock as it effects a gauge carrier or the like. U.S. Pat. No. 2,577,599 is an early teaching of a shock proof case providing wireline support of an instrument housing assembly through a series of resilient elastomeric isolation pads.
U.S. Pat. No. 3,714,831 exemplifies the types of device that function to carry a measuring instrument suspended within such as a drill collar section that is designed to receive the instrument. Once again, an elastomeric body or series of annular bodies disposed between the instrument and the drill-collar frame provide reduced vibration suspension of the measuring instrument. This type of device also allows for central passage of drilling fluid through the drill collar simultaneous with sensing operations. A U.S. Pat. No. 4,628,995 discloses a carrier for supporting pressure gauges on a tool string while providing seating for one or more pressure gauges. This device utilizes a restricted flow passageway that impedes the flow of hydraulic well fluid under the effect of the pressure surge at detonation of a perforator, and subsequent expansion of the fluid pressure in an enlarged bore section damps the pressure surge to safely isolate the pressure-sensitive components.
Therefore, it is an object of the present invention to provide rapid damping of the effects of the shock forces produced by jet detonation that travel either upward or downward relative to the tool string.
It is also an object of the invention to provide a shock isolation mechanism that safeguards against shock generation either above or below a preselected point in the tool string.
It is still another object of the present invention to greatly reduce or eliminate sudden shock loading requirements thereby to protect delicate instrumentation in the tool string.
Finally, it is an object of the present invention to provide a shock absorber that is capable of very rapid displacement and subsequent shock absorption.
Other objects and advantages of the invention will be evident from the following detailed description when read in conjunction with the accompanying drawings which illustrate the invention.